1. Field of the Invention
The present invention relates to a magnetic garnet single crystal grown by the liquid phase epitaxial process (LPE process) and a Faraday rotator using the same.
2. Description of the Related Art
Faraday rotator is used as an optical element for rotating the polarization direction of light to 45 degrees (deg.) in optical isolators, optical circulators and the like for communication. Faraday rotator is generally prepared by polishing a magnetic garnet single crystal grown by the LPE process to a Faraday rotation angle of 45 deg. and then preparing an antireflection film on the face thereof for optical incidence/emission.
As a solvent in growing a magnetic garnet single crystal by the LPE process, lead oxide (PbO) is used together with boron oxide (B2O3) and bismuth oxide (Bi2O3). During the growth of the magnetic garnet single crystal, therefore, a small amount of lead (Pb) contaminates the resulting crystal.
So as to comply with the recent environmental regulations, however, efforts are now directed toward the reduction of the content of Pb as an environmental load substance in such Faraday rotators. Consequently, a technique for using sodium (Na) in place of Pb as a solvent material for growing a magnetic garnet single crystal by the LPE process is under way of establishment. See non-patent reference 1: PARK J. H., Growth of epitaxial garnet film by LPE for application to integrated magneto-optic light switch arrays, Physica Status Solidi A: Applied Research, June 2004, Vol. 201, No. 8, pp. 1976-1979, CODEN: PSSABA: ISSN: 0031-8965.
When Na is used as the solvent, however, a small amount of Na contaminates the resulting garnet single crystal film, leading to the occurrence of optical absorption in the single crystal. Then, a Faraday rotator prepared from the garnet single crystal with such optical absorption has an increase in the optical loss. When a Faraday rotator with a large optical loss is used to prepare an optical device for communication, such as optical isolator, the device profile is disadvantageously deteriorated.
Therefore, the optical loss is now reduced by adding elements becoming tetravalent cations (positive ions) for the charge compensation together with Na, including for example Si, Ge, Ti and Pt, to such garnet single crystal.
However, it has been found that simple addition of such tetravalent cations stable at those valence states causes a large variation of the optical loss of the resulting Faraday rotators, so that not any Faraday rotators with optical losses reduced at their minimums can be produced at high reproducibility.
Devices such as in-line optical isolator toward which a small optical loss is required should require a Faraday rotator with a particularly low optical loss. For such use, it is an issue to produce a Faraday rotator with a small optical loss at high reproducibility.